one mans severe turbulence is another mans medium turbulence
I only ever experienced severe turbulence once and that was coming out of Nice on a Northerly Sid in a empty corporate jet.
On the approach into Nice we were warned of severe turbulence between FL200 and FL300
I felt an idiot warning the Pax of a rough ride ahead, getting them strapped in and reducing the speed right back to find smooth air all the way to the ground
" Where was all that turbulence" Was the owners reply looking at me as if I was some sort of paranoiac idiot.

We left the PAX there and took the jet back empty. In the climb passing FL200 all hell let loose,with cupboards flying open all the contents being hurled from one end of the cabin to the other.
Autopilot disconnected wing drops were 45 degrees with the aircraft tossed around like a puppet and almost uncontrollable.
The VSI normally showing 1000 fpm at that level was showing a solid 2500 fpm all the way to FL300 where the air went silky smooth
The usual is PIREPS but even those cannot show you isolated patches of very severe air only giving a picture of what lies ahead

Many years ago [the 1980s?] the Met Office led research into CAT and one remark from a leading scientist managed to stick:

"One aircraft reports severe CAT, exact location and height, and we go straight away to find it. Never did find it. Severe CAT is like a shoal of fish in a big ocean".

Not surprising because a lot of CAT is in effect comparable to an earthquake in that we are witnessing a sudden release of strains, tensions, which may or may not rebuild.

This is being discussed on Jeremy Vine on Radio 2 right now, and the 747 pilot who has just been speaking has left me, as SLF, a little confused.

I've a good grasp of physics (which is why I'm not concerned by turbulence, even on the one 'extreme' experience I've had) and can understand the pilot referring to the plane as following a pressure wave. However, he was adamant that the plane does not lose altitude.

If you're in a large metal tube and suddenly hit the ceiling, then that metal tube must surely have dropped by at least around 12 feet. If you're left attached to the ceiling for a few seconds, the tube must be dropping further, surely?

I completely accept that the perception of dropping 'thousands of feet' is out of line, but am I taking this pilot too literally? During extreme turbulence events, what kind of altitude change can there be?

You and me both Phil. If the aircraft hasn't lost any altitude but you're stuck to the ceiling then you must have gained altitude, how does that work?

The gentleman reporting on this UA incident may have mis-heard a directive from the FD or purser to the flight attendants, or intended for standing passengers only, not as a general instruction


Agree, I am sure the instruction, misheard, would be "anyone out of their seats, get on the floor immediately" not everyone get out of their seats, etc.

Probably an FSX B747 pilot! :E

I listened to Mr vine on the drive home. The Irish reporter with his conviction that it was down to 'air pockets' was just as plausible as the ex 747 driver.:O

made some quick notes (so not a full and complete transcript) from an available short interview with one of the pax on board - who says he has not seen anything like this in his 30 years of flying - gives some background to some of the items discussed in this thread:

..... Middle of the night, 4 hrs out from Heathrow over the Atlantic to US,this tremendous turbulence happened, the word turbulence is not strong enough, there should be another word for it .... plane fell, 4x dramatic drops, 1st one(about a 1,000ft) after short shudder, then 3 other drops, most people sleeping with seatbelts on, woke everyone up immediately of course, babies crying, ... pilots said we had no warning, did not see this coming, ref’d Atlantic storm, pilots say do not expect more, but pax find that not reassuring, rest of flight was fine except “a few little shudders". Stewardess in galley area hit head bleeding along arm, guy standing next to her fell on floor, lot of people injured .....

This pax does not mention being told to sit down.

In the handful of cases where I've experienced moderate- to severe-turbulence, the pilot usually told PAX to go back to their seats, buckle their seat belts and flight attendants to take their seats.

Better to "err" on the side of caution!

The day of my flight, I usually consult http://apps.turbulenceforecast.com/. Obviously, these conditions can change by the minute, but I've at least got an idea of what to expect when flying and keep my seat belt fastened accordingly.

To inform Pace and others, there have long been accepted descriptors of turbulence. When the level of turbulence is reported in a PIREP, it is important to consider the type of aircraft that encountered said turbulence. Altitude also gives a clue at what airspeed the turbulence was encountered. If the aircraft was on approach, the airspeed was most likely below 250 kts. CAT is usually encountered at cruise, so for a jet airliner, the airspeed was probably in excess of 400 kts.

Remember that CAT usually occurs at the intersection of the Jet Stream core, the tropopause and the borders of a warm and cold air mass. An aberrant eddy of air is thought to mix up the Jet Stream core with the resultant turbulence. Because CAT it is transient, i.e. dynamic, it is nearly impossible to track and predict. Way back in the 1960's, Northwest Orient Airlines researched CAT, with their airliners equipped with special sensors. A CAT reporting program was a result of the study. Conclusion(s): At cruise, CAT was almost always encountered just before a sudden and rapid increase in OAT (Outside Air Temperature). It was nearly impossible to anticipate. Subsequently, NWA installed an audible and visual warning system to alert pilots of impending CAT based on a rapid increase of OAT at cruise. The CAT in-flight warning system never caught on for several reasons.

LEVELS OF TURBULENCE: Aircraft Reaction and What Occupants feel:

Level 1, Light Turbulence that momentarily causes slight, erratic changes in altitude and/ or attitude (pitch, roll, yaw) Occupants may feel a slight strain against seat belts or shoulder straps. Unsecured objects may be displaced slightly. Food service may be conducted and little or no difficulty is encountered in walking.

Level 2, Moderate This will cause changes in accelerometer readings of around 0.5 – 1.0g at the aircraft’s centre of gravity. Changes in altitude and/ or attitude occur but the aircraft remains in positive control at all times. It usually causes variations in indicated airspeed Occupants feel definite strains against seat belts or shoulder straps. Unsecured objects are dislodged. Food service and walking are difficult.

Level 3, Severe This will cause changes in the accelerometer reading of greater than 1g at aircraft’s centre of gravity. Large, abrupt changes in altitude and/ or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control Occupants are forced violently against seat belts or shoulder straps. Unsecured objects are tossed about. Food services and walking are impossible.

Level 4, Extreme Turbulence in which the aircraft is violently tossed about and is practically impossible to control.

Evanssb

Thanks for that detail )) just to add severe turbulence can also come from mountain wave to many thousand of feet above the Mountain range altitude

And you hear so many from the West side of the Atlantic calling moderate and severe when really it is light at the most!!

As you might guess from my log-in name I am "concerned" when the aircraft I am in hits turbulance.
Do any of you experts think that the amount of turbulance has increased over the last 50 years or so
or is it just more wimps like me noticing it ?

Years ago I heard one of out TransAtlantic friends say "I don't know what you'd call this turbulence, but I've got whitecaps on my coffee".

Wave is also paradoxically super smooth when in the lift zone; I once flew from the Peak District past Nottingham hopping from one wave bar to the next, climbing in each in my little unpowered hang glider in such smoothness in a clear evening sky that it felt I was hanging from some invisible hook, and next day i noticed the left side of my face was noticbly more sun burned than the right side, from the steady oritentation whilst climbing. And yes, under the wave it is not a nice place to be on any small craft.

The worst turbulence I ever experienced was over the Bay of Bengal flying with MAS. It was so severe that the CC were strapped in and had their 'fixed grin' faces on, which actually worried me even more. :eek:

We had warning of the conditions as the seat belt signs came on 10 minutes before we started getting shaken about. But it got worse and the pilot decided he'd had enough.

He didn't do a 180, more a 120, which looked very odd on the skytracker thingy but I've always thought that for the pilot to do such a drastic change of course it meant that he was finding things very hairy. At no stage did he talk to us, fair enough in the turbulence, but not afterwards either. :confused:

The Bay of Bengal of course does not always have the smoothest flying conditions in the world!

Ironically, the worst turbulence I have ever experienced when was as a passenger at 12 or 13 years old flying from DFW to LAX, as our family was on the way to Maui. My father flies 100+ segments a year, and when we talk about a rough flight it's always compared to that event. It happened maybe 45 minutes out of DFW in clear air. It had been a rough flight until then so everyone was belted including the crew. Drinks and meals hit the ceiling, some passengers were screaming, it was insane. I'd be surprised if there wasn't a loss of more than 250 feet during the episode.

Vollibre

Mountain wave can be smooth but can be far from smooth ))

Jeremy Vine. Again...
 

Oh dear.
For the SLF understandably confused: Yes, the "ex 747" guy could have been a little clearer.
He was trying to make the point about the aircraft dropping thousands of feet into imaginary air pockets. He came across as suggesting there will be no altitude change at all. Of course this is never true, even in normal flight.
It only takes an altitude change equal to the diameter of the cabin for everything to hit the roof, if the change is sudden enough.

Even Fox news clears this up:
https://www.google.co.uk/url?sa=t&rc...S5bw8pxpDM-M3g

Then he (Vine) goes on:
"Is that why catering trolleys are so heavy?"
(So they won't float up in negative g)
Good grief.
Did he actually go to school?

More flights = more chance of noticing